1. FIELD OF THE INVENTION
This invention relates to a powdered leather and a method of producing the powdered leather, and more particularly to a powdered leather which has an ultra-small particle size and contains few impurities and a method of producing the last-named powdered leather. The powdered leather is useful when mixed in resin when manufacturing various products such as coating (paint), leather (synthetic leather or artificial leather), film, sheet, fibers and moldings.
2. DESCRIPTION OF THE RELATED ART
In the manufacture of natural-leather-like articles such as coatings, films, sheets or fibers (yarns), it has hitherto been customary that a powdered leather is mixed in resin, and then this mixture is coated over a substrate or is molded. In the past, the powdered leather to be used was produced by grinding a powdered animal leather raw material such as shapings into coarse particles using a grinding means such as a hammer crasher.
However, with this simple mechanical grinding means, since the powder particles tend to stick to one another to form relatively massive or fibrous lumps, only coarse grains could be obtained. If the particle size of the powdered leather is large, various restrictions (e.g., the thickness of a coating, sandy touch of the surface and breakage of a yarn) would be inevitable in various applications, constituting obstacles to manufacturing.
To this end, various solutions have been proposed which are exemplified by the following: Japanese Patent Laid-Open Publication No. 63-156552/1988 discloses a method in which the powdered leather raw material ground into coarse particles is swollen in steam (hereinafter called "steam-boiling"), whereupon the swelled coarse particles are dried and then pulverized. Japanese Patent Laid-Open Publication No. 63-99298/1988 discloses an apparatus in which the powdered leather raw material is ground into coarse particles, whereupon the coarse particles are boiled, dried, pulverized and classified. Japanese Patent Laid-Open Publication No. 63-286499/1988 discloses a method in which the powdered leather raw material is defatted using a solvent, whereupon the resulting raw material is steam-boiled, dried and pulverized. Practically, in Japanese Patent Laid-Open Publication No. 63-233828/1988 the thus obtained fine particles are used in a molded product as fine powder of at most 40 .mu.m size. Further, in Japanese Patent Laid-Open Publication No. 1-314789/1989 the fine particles are used in a synthetic leather as fine powder of at most 30 .mu.m particle size.
According to the foregoing method, the fine particles include those having a particle size of at least 10 .mu.m and are hence unsuitable to be mixed in a thin film, a coating or fibers. Specifically, a thin film generally requires a particle size of 5 to 200 .mu.m. A synthetic leather in which a synthetic resin layer containing the powdered leather is coated over the surface of a substrate requires a particle size of 5 to 30 .mu.m. Coating and fibers generally require a particle size of at most 10 .mu.m, preferably as small as possible.
Conventionally, no consideration has been made about impurities except collagen usually contained in leather, for example, concerning amounts and kinds; while a finished product manufactured using the foregoing powdered leather is used or stored for a long time period, impurities would be bled out to the surface as influenced such as by humidity and heat, thus deteriorating the appearance and the anti-discoloration properties of the product.
It is therefore an object of this invention to provide a powdered leather which is suitable for use when manufacturing a thin film, a coating, fibers, etc. and which can reduce deterioration of the appearance and properties of a finished product, thus providing an improved degree of durability.
Another object of the invention is to provide a product manufactured using the powdered leather described above.
Still another object of the invention is to provide a method of producing the powdered leather described above.